The present invention provides a column tilt apparatus and method for providing an off-normal angle of incidence of a beam in a scanned beam system onto a substrate passing through the eucentric point that is electro-mechanically adjustable during operation while maintaining vacuum integrity of the column and work chamber, and without introducing significant vibrations.
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1. A method for moving a beam column of a beam system through an interval of angular displacement, comprising the steps of:
providing a first subassembly affixed to a vacuum chamber and having a first opening; providing a second subassembly to which a beam column is affixed, the second subassembly having a second opening and being electro-mechanically drive-able through a path of angular displacement with respect lo the first subassembly; and providing a vacuum seal between the first opening and the second opening.
10. An apparatus for moving a beam column of a beam system through a path of angular displacement, comprising:
a first subassembly affixed to a vacuum chamber and having a first opening; a second subassembly to which the beam column is mounted, the second assembly having a second opening: an electro-mechanical drive system to electro-mechanically drive the second subassembly through a path of angular displacement with respect to a position of the first subassembly; and a vacuum seal between the first opening and the second opening.
20. A beam system for interacting with a work piece, comprising:
a first subassembly affixed to a vacuum chamber and having a first opening; a second subassembly to which the beam column is mounted, the second assembly having a second opening; an electro-mechanical drive system to electro-mechanically drive the second subassembly through a path of angular displacement with respect to a position of the first subassembly; a vacuum seal between the first opening and the second opening and a beam column mounted to the second subassembly for generating a beam to interact with the work piece.
2. The method of
4. The method of
5. The method of
providing a motor mounted to one of the two subassemblies with a first gear mounted to a rotatable shaft of the motor; and providing a second gear enmeshed with the first gear and mounted to the opposite subassembly to which the motor is mounted; whereby rotation of the shaft causes relative motion between the subassemblies.
6. The method of
7. The method of
providing a mechanism to limit the extent of displacement.
8. The method of
providing an air bearing between conformal opposing surfaces of the two subassemblies.
9. The method of
11. The apparatus of
12. The apparatus of
13. The apparatus of
15. The apparatus of
a motor mounted to one of the two subassemblies with a first gear mounted to a rotatable shaft of the motor; and a second gear enmeshed with the first gear and mounted to the opposite subassembly to which the motor is mounted; whereby rotation of the shaft causes relative motion between the subassemblies.
16. The apparatus of
18. The apparatus of
19. The apparatus of
an air bearing between conformal opposing surfaces of the two subassemblies.
21. The system of
22. The system of
23. The system of
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The present invention relates to the field of scanned beam systems, and in particular, to a method and apparatus for tilting a beam column.
Scanned beam microscopy systems, including charged particle beam systems such as electron beam and focused ion beam (FIB) systems, are widely used in characterization or treatment of materials on a microscopic scale. For example, focused ion beam systems are used in manufacturing operations because of their ability to image, etch, mill, deposit and analyze with great precision. Ion columns in FIB systems using gallium liquid metal ion sources (LMIS), for example, can provide five to seven nanometer lateral imaging resolution.
The beam of a scanning beam system typically scans the surface of a target specimen in a raster pattern. This raster pattern may be used to produce an image of the surface of the target. When the scanned beam strikes the target, particles or photons are emitted from the immediate vicinity of beam impact. A portion of these emissions are measured or collected using a suitable detector or collector that produces an output signal indicative of the intensity of the emission. This output signal is then processed to produce an observable image displayed on a conventional video monitor.
A typical application of scanning beam systems is for analysis and treatment of integrated circuits (IC). In this application, a focused ion beam is used to produce an image of the circuit. This image is then used in conjunction with circuit layout information to navigate the ion beam over the surface of the circuit to locate a specific element or feature of interest. When the beam is scanned to the local area of interest, the beam current can be increased to cut into the circuit die and expose circuit features buried in layers. The FIB system can then alter the exposed circuit by cutting conductive traces to break electrical connections or by depositing conductive material to provide new electrical connections. This etching or deposition is caused by a physical or chemical reaction of the beam ions with the specimen and occurs at a rate that is largely dependent upon the constituent ions of the beam, the presence and type of etch enhancing or deposition precursor gases, and the beam current.
Although the typical focused beam system configuration provides a beam that impinges normal to the substrate, focused beam systems may be used in tilt orientations, in which the beam impinges at an off-normal angle of incidence with respect to the plane of the substrate to perform ion beam milling or electron beam viewing at a specified angle. Although this could be accomplished by tilting the stage that contains the working piece to be viewed or etched, there is difficulty in maintaining coincidence between the center point of beam impact and the axis of stage rotation for all desired angles of incidence.
Alternatively, a change in angle of incidence could be obtained by tilting the beam column about an axis of rotation passing through the working piece at the desired center point of beam impact. But prior art methods do not provide a satisfactory way to provide a change in column tilt angle without interrupting system operation. Prior art methods for providing column tilt to produce an off-normal angle of incidence include the use of fixed tapered spacers in conjunction with vacuum seals to set the incidence angle of the beam. To expose the working piece to successive incidence angles, one must iteratively change the spacers used to set the angle of column tilt. Changing the tapered spacers required exposing the sample chamber, thereby requiring additional time to evacuate the chamber and restart and stabilize the emitter after the tilt angle is changed. An alternative prior art method employs a bellows that purportedly enables the system to remain sealed while the column is mechanically tilted, but the change in tilt angle must be performed manually and is difficult to rapidly set to a precise angle of tilt.
It is desirable to have the beam remain focused at the same point on the work piece throughout a range of column tilt angles. This can be achieved by tilting the beam about the point at which the beam is focused to maintain a constant "eucentric point." A "eucentric point" is defined as an arbitrary point through which the beam passes when it is not being deflected and that is a specified distance from the axis of beam deflection. The eucentric point is preferably chosen to coincide with the center point of beam impact and the eucentric point preferably stays at the same location in space for all angles of column tilt. Prior art methods do not provide a satisfactory method of achieving this constant eucentric point. Further, prior art methods do not provide a satisfactory way to provide a change in tilt angle without interrupting system operation. It would therefore be desirable to provide a system and method that enables column tilt over a range of tilt angles during system operation while maintaining a constant eucentric point that overcomes prior art limitations.
The present invention overcomes prior art limitations by providing a method and apparatus for automated adjustment of the tilt angle of a beam column during operation of a scanned beam system over a continuous angular sector, while maintaining a constant eucentric point, maintaining vacuum integrity of the column and work chamber, and without introducing significant vibrations.
According to the present invention, a beam column can be driven electro-mechanically throughout a range of angular displacement to enable precise control of the angle of tilt while maintaining a constant eucentric point. The electro-mechanical drive system can be controlled by computer to provide a desired sequence of angular displacements through which the column is tilted during operation of the beam system. Air bearing support is provided to minimize friction and vibration in the system and a unique bellows is employed to maintain a vacuum or low-pressure environment as the column is tilted
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter. It should be appreciated by those skilled in the art that the disclosure provided herein may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Persons of skill in the art will realize that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims, and that not all objects attainable by the present invention need be attained in each and every embodiment that falls within the scope of the appended claims.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
The present invention provides a method and apparatus for automated adjustment of the tilt angle of a beam column during operation of a scanned beam system over a continuous angular sector, while maintaining a constant eucentric point, maintaining vacuum integrity of the column and work chamber, and without introducing significant vibrations.
The present invention will be discussed in the context of use in a focused ion beam system for demonstrative purposes. However, it will be understood that the methods of the present invention may also be employed in other scanned systems, such as electron beam systems including scanning electron microscopes and scanning transmission electron microscopes.
In
High voltage power supply 34 is connected to liquid metal ion source 14 as well as to appropriate electrodes in focusing column 16 for forming an approximately 1 keV to 60 keV ion beam 18 and directing the same downwardly. Deflection controller and amplifier 36, operated in accordance with a prescribed pattern provided by pattern generator 38, is coupled to deflection plates 20 whereby beam 18 may be controlled to trace out a corresponding pattern on the upper surface of specimen 22. In some systems the deflection plates are placed before the final lens, as is well known in the art.
The source 14 typically provides a metal ion beam of gallium, although other ion sources, such as a multi-cusp or other plasma ion source, can be used. The source typically is capable of being focused into a sub-one-tenth micron wide beam at specimen 22 for either modifying the surface 22 by ion milling, enhanced etch, material deposition, or for the purpose of imaging the surface 22. A charged particle multiplier 40 used for detecting secondary ion or electron emission for imaging is connected to video circuit and amplifier 42, the latter supplying drive for video monitor 44 also receiving deflection signals from controller 36. The location of charged particle multiplier 40 within chamber 26 can vary in different embodiments. For example, a preferred charged particle multiplier 40 can be coaxial with the ion beam and include a hole for allowing the ion beam to pass. A scanning electron microscope 41, along with its power supply and controls 45, are optionally provided with the FIB system 8.
A fluid delivery system 46 optionally extends into lower chamber 26 for introducing and directing a gaseous vapor toward sample 22. U.S. Pat. No. 5,851,413 to Casella et al. for "Gas Delivery Systems For Particle Beam Processing," assigned to the assignee of the present invention, describes a suitable fluid delivery system 46.
A door 60 is opened for inserting specimen 22 on stage 24 which may be heated or cooled and also for servicing a reservoir if one is present. The door is interlocked so that it cannot be opened if the system is under vacuum. The high voltage power supply-provides an appropriate acceleration voltage to electrodes in ion beam column 16 for energizing and focusing ion beam 18. When it strikes specimen 22, material is sputtered, that is physically ejected, from the sample. Focused ion beam systems are commercially available, for example, from FEI Company, Hillsboro, Oregon, the assignee of the present application. Signals applied to deflection controller and amplifier 36 cause the focused ion beam to move within a target area to be imaged or milled according to a pattern controlled by pattern generator 38.
A preferred embodiment of the present invention is shown in perspective view in
Attached to assembly 2200 is a motor 2220 and a gear unit 2240. A side view of column tilt apparatus 2000 is shown in FIG. 3A. Motor 2220 is attached to a gear 2212. Gear 2212 is enmeshed with a gear 2215. Gear 2215 is attached to a smaller gear 2216, as shown in
A side view of gear unit 2240 is shown in FIG. 4. Gear unit housing 2242 is attached to, and moves with, assembly 2200. Passing through gear unit housing 2242, and free to rotate there within against ball bearings 2244, is a shaft 2246 to which gears 2215 and 2216 are attached at one end. When motor 2220 is caused to rotate, gear 2212 rotates. The rotation of gear 2212 causes gear 2215 and 2216 to also rotate. Since gear 2216 is enmeshed with gear segment 2111, which is attached to stationary assembly 2100, assembly 2200 is forced to move.
Referring again to
Motor 2220 is controlled by electrical signals that correspond to a desired angular displacement of the beam column. Thus, while the beam system is in operation, the angular displacement of the beam column can be adjusted by a controlled changed in the electrical signals driving motor 2220. When gears 2215 and 2216 are caused to rotate, shaft 2246 is also thereby caused to rotate. At the end of shaft 2246 that is opposite to the end that gears 2215 and 2216 are mounted, is mounted a flag 2248, shown in FIG. 4. Flag 2248 rotates with shaft 2246. Referring to
Friction between surfaces 2150 and 2250 is preferably eliminated, or at least minimized, by an air bearing; that is, pressurized air is applied to cause assembly 2200 to be lifted above assembly 2100 by a small amount, e.g., 10 microns, and even less than 2 micrometers, to prevent frictional contact between surfaces 2150 and 2250 and further to minimize vibration. Persons of ordinary skill in the art will recognize other methods for reducing vibration and friction between assemblies 2100 and 2200, given the disclosure herein.
Inserted and mounted within cylindrical bore 2800 is a bellows that enables motion between assemblies 2100 and 2200 While maintaining vacuum in the focused beam system. A perspective view of a bellows assembly 2300 is shown in
Also partially shown in
The upper end of bellows subassembly 2350 is welded to flange structure 2320 and the lower end of bellows subassembly 2350 is welded to a cylindrical structure 2370. Similarly, the lower end of bellows subassembly 2360 is welded to flange structure 2340 and the upper end of bellows subassembly 2360 is welded to cylindrical structure 2370. When subassembly 2200 is caused to move with respect to subassembly 2100, bellows subassemblies 2350 and 2360 expand and contract in accordion-like manner. Cylindrical structure 2370, which may be formed of thin steel, prevents any particulate matter from entering into its interior, thereby preventing contamination within the system.
O-rings are also employed to maintain a vacuum seal between the bellows assembly and the beam column on one side and the system vacuum chamber on the other side. In particular, an O-ring groove 2380 shown in
The bellows 2300 can be constructed to provide at least 5 degrees and preferably 10 degrees of angular displacement of assembly 2200. This is advantageous when the contour of a feature etched into a substrate is important. For example, during the fabrication of integrated circuits, it is common to etch a part of a circuit using a focused ion beam system to expose a cross section of the various layers of the circuit. If the etched wall is curved or not perpendicular to the surface, a cross sectional view of the exposed surface will be distorted. To maximize resolution of the imaged cross section, the etching is preferably straight down, perpendicular to the surface of the wafer on which the integrated circuit is formed.
Because the current distribution across the focused ion beam in not uniform, a vertical focused ion beam does not etch an edge that is perpendicular to the surface.
Thus, tilting a charged particle beam column provides a method for producing an etched wall that is approximately perpendicular to a work piece surface so that a high-resolution image of the exposed wall be obtained. Although the same effect could be accomplished by tilting the stage, tilting stages have several disadvantages as described in U.S. Pat. No. 6,039,000, "Focused Particle Beam System and Methods Using a Tilt Column," which is assigned to the assignee of the present application.
The geometry of motion provided by the above-described system is illustrated in
As noted above, motor 2220 is controlled by electrical signals that correspond to a desired angular displacement of the beam column. Thus, while the beam system is in operation, the angular displacement of the beam column can be adjusted by a controlled changed in the electrical signals driving motor 2220. Motor 2220 and associated electrical signals can be implemented to continuously--or in steps, in the case of a stepping motor--drive the moveable subassembly electro-mechanically through a desired angular displacement from its current position or to a particular desired angle of tilt.
A desired sequence of angular displacements through which the column is tilted during an interval of time can be implemented in software to program a microprocessor, or other programmable machine, to cause electronic circuitry within a motor control subsystem to generate the electrical signals required to drive the column through the desired sequence. A user of the system can program the sequence by way of an information display apparatus and an information entry apparatus such as, for example, a video monitor and keyboard.
The system user controls the tilt of the column by entering information through a keyboard that can be displayed on a video monitor, and transmitted to a computer. The computer can be caused by information transmitted to it to initiate a sequence of outputs that cause the motor control subsystem to generate signals that drive subassembly 2200 through a desired sequence of angular displacements.
The beam column of the system is mounted to subassembly 2200 in an orientation that aligns the axis of the beam emitted by the beam column with the tilt axis of subassembly 2200. The emitted beam therefore passes through an interior region of the chamber to impact the work piece affixed to the work station in the chamber at the currently desired angle of incidence. Embeddable in the computer is a software program that enables control of, not only tilt angle, but also the rate at which angular displacement occurs. The computer be programmed to control the dwell time at a fixed angle of tilt between successive changes in tilt angle.
Further, the computer can be programmed to control movement and rate of movement of the work station. Thus, control of the relative orientation and relative rate of motion between the work station and the beam of the beam column is provided. Additionally, the emission of the beam can be caused to cease for a controllable and specifiable interval of time. Therefore, the beam can be "turned off" if desired when, for example, relative motion between the beam column and the work station occurs.
The system of the present invention may further comprise an imaging subsystem comprising an imaging beam source and a detector. The imaging beam source and detector are disposed at such angles and distances with respect to the work station as to enable imaging of the work piece, without interfering with the beam emitted by the beam column. In an alternative embodiment, the imaging beam source may be the beam column mounted to subassembly 2200 to enable imaging at selectable desired tilt angles. A detector generates signals in response to emissions received from the work piece. These signals may then be processed and sent to a video monitor to display an image of the work piece.
Thus, the present invention provides an automate-able electro-mechanical drive system to drive a beam column through a pre-determinable sequence of displacements. Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, and without limitation, persons of ordinary skill in the art will readily see that the electro-mechanical drive system described herein could also include hydraulic elements. A linear motor could be used in substitution of the rotary motor described above. A mechanically activated disconnect switch could be used instead of or in addition to the sensors employed to limit the extent of displacement of the apparatus.
The invention achieves multiple objectives and because the invention can be used in different applications for different purposes, not every embodiment falling within the scope of the attached claims will achieve every objective. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
Tanguay, Michael, Groholski, Alexander, Drainoni, Riccardo
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